Servo-actuator mechanism

ABSTRACT

In a servo-actuator mechanism of a pull type, fluid pressure is applied to the annular area of an annular piston guided on its inside and outside diameters by an internal cylindrical portion and an outer tube, respectively, of the actuator cylinder structure. High pressure seals are provided at the inside and the outside diameters of the annular piston. A piston rod, which extends through the internal cylindrical portion, is attached to the low pressure end of the piston, and two low pressure piston rods seals are provided to prevent leakage of the fluid from the actuator cylinder. A fast dumping action is achieved by means of a hydraulically closed, spring and hydraulically opened dump valve.

iJnited States Lewis ate [191 1 1 Apr. 10, 1973 [73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Feb. 22, 1971 [21] App1.No.: 117,252

[56] References Cited UNITED STATES PATENTS 7/1957 Swartwout et a1 ..9l/454 9/1962 Kintner l ..92/l08 10/ 1 966 Phillips, Jr ..9l/454 Primary Examiner-Paul E. Maslousky Attorney-A. T. Stratton, F. P. Lyle and F. Cristiano [57] ABSTRACT In a servo-actuator mechanism of a pull type, fluid pressure is applied to the annular area of an annular piston guided on its inside and outside diameters by an internal cylindrical portion and an outer tube, respectively, of the actuator cylinder structure. High pressure seals are provided at the inside and the outside diameters of the annular piston. A piston rod, which extends through the internal cylindrical portion, is attached to the low pressure end of the piston, and two low pressure piston rods seals are provided to prevent leakage of the fluid from the actuator cylinder. A fast dumping action is achieved by means of a hydraulically closed, spring and hydraulically opened dump valve.

4 Claims, 5 Drawing Figures PAIENTEU APR 1 0 ma SHEET 1 1F 2 FIG. 2

SERVO-ACTUATOR MECHANISM BACKGROUND OF THE INVENTION This invention relates, generally, to servo-actuator mechanisms and, more particularly, to hydraulically operated actuators of a pull type suitable for actuating a control valve for a steam turbine.

In order to eliminate external linkage between the hydraulic servo-actuator and the control valve for a steam turbine, it is necessary to mount the actuator above the steam chest directly in line with the control valve. Such a mounting arrangement requires the prevention of leakage of the high pressure operating fluid from the servo-rod exit onto the external parts of the structure. It is also desirable that the actuator be capable of fully stroking in a relatively short period of time.

BRIEF SUMMARY OF THE INVENTION In accordance with one embodiment of the invention, movement of an annular piston in an actuator cylinder is guided on its inside and outside diameters by an internal cylindrical portion and an outer tube, respectively, of the actuator cylinder structure. Fluid pressure is applied to the annular area of the piston and high pressure sealing rings are provided at the inside and the outside diameters of the annular piston. A piston rod extends through the internal cylindrical portion and is attached to the piston in the low pressure region. Low pressure seals are provided at the entrance of the piston rod into the cylindrical portion, thereby preventing leakage of the operating fluid from the actuator cylinder. A positive opening dump valve which is fluid pressure is provided.

BRIEF DESCRIPTION OF THE DRAWING For a better understanding of the nature of the invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a view, in longitudinal section, of a steam control valve structure and hydraulic actuator embodying principal features of the invention;

FIGS. 2 and 3 are enlarged fragmentary views of seal structures utilized in the hydraulic actuator;

FIG. 4 is an enlarged view, in section, of a dump valve structure provided for the actuator shown in FIG. 1, the dump valve being in the closed positon, and

FIG. 5, is a view, similar to FIG. 4, showing the dump valve in the open position.

DESCRIPTION OF PREFERRED EMBODIMENT Referring to the drawing, particularly to FIG. 1, the structure shown therein comprises a steam control valve 10, a spring housing and support column 12 mounted on the valve 10, a hydraulic actuator 14 mounted on the spring housing 12 directly above and in line with the valve 10, and a dump valve 15 mounted on one side of the actuator 14. The valve 10 may be of a type well known in the art suitable for controlling the flow of steam to a steam turbine. The valve includes a generally cup-shaped body 16 and a cover 18 attached to the body 16 by bolts 20. The body 16 has an inlet port 22 and an outlet port 24. The inlet port 22 may be connected to a suitable supply of steam (not shown) and the outlet port 24 may be connected to a steam turbine (not shown). A valve seat 26 is provided at the inner end of the outlet port 24.

As shown, the outlet port 24 is closed by a valve member 28 of the plug type seated in the valve seat 26. The valve member 28 has a stem 30 extending upwardly through a bearing 32 mounted in the valve cover 18. The upper end of the valve stem is attached to'the lower end of a piston rod 34 by means of a coupling member 36 disposed inside the spring housing 12. The coupling 36 also serves as a support for a plucludes an outer tube 48 extending between a base 50 and a cylinder head 52. The base 50 is mounted on a seal ring 54 attached to the cover 40 of the spring housing 12 by means of bolts 56. The base 50 and the cylinder head 52 are attached to the seal ring 54 by means of through bolts 58. The outer tube 48 is retained between the base 50 and the cylinder head 52 by means of the bolts 58. O-rings 60 and 62 are provided where the cylinder 48 is seated in the base 50 and the head 52, respectively.

As shown, an upwardly extending internal cylindrical portion 64 is formed integrally with the base 50 and spaced from the outer tube 48. A rectilinearly movable annular piston 66 surrounds the cylindrical portion 64 in the space between the tube 48 and the internal cylindrical portion. An annular high pressure chamber 68 is provided in the base 50 around the internal cylindrical portion 64 for receiving a high pressure actuating fluid to apply pressure on the lower end of the annular piston 66. The pressurized actuating fluid is admitted to the chamber 68 through a conduit 70 which may be connected to a suitable supply of pressurized fluid (notshown). The piston rod 34 extends upwardly through the internal bore of the cylindrical portion 64 and is attached to the upper end of the piston 66 by means of a pin 72. An enlarged head 74 on the upper end of the piston rod 34 engages the upper end of the annular piston 66.

As explained hereinbefore, it is essential that leakage of the pressurized actuating fluid from the actuator 14 be prevented. In order to accomplish this, first high pressure seal means 76 is disposed between the annular diameter of the internal cylindrical portion 64. The seal rings 78 contact the inner surface of the annular piston 66. Thus, the high pressure actuating fluid is normally retained in the high pressure region below the annular piston 66 by the high pressure seal means. Furthermore, the high pressure seal means '76 and 78 guide the movement of the annular piston 66 since the lengths of the internal cylindrical portion 64 and the annular piston 66 are each greater than the stroke length of the actuator.

With a view to still further reducing the possibility of leakage of the high pressure actuating fluid from the actuator, low pressure seal means 80 is disposed at the entrance of the piston rod 34 into the internal cylindrical portion 64. Additional, low pressure seal means 82 is provided at the exit of the piston rod 34 from the internal cylindrical portion 64. A rod wiper seal 84 may be provided below the low pressure seal 82. The seals 82 and 84 are mounted in the seal ring 54. The seal 80 is mounted in the upper end of the internal cylindrical portion 64. In this manner, the piston rod is sealed at both ends, thus protecting the low pressure fluid seal and corresponding rod sealing length with the exit seal.

As shown more clearly in FIG. 2, the seal means 80 includes a seal member 81 mounted in a flanged retainer 83 and a seal member 85 in a threaded retainer 87. The retainer 87 is threaded into the upper end of the internal cylindrical portion 64. A compression ring 89 is disposed between the seal members 81 and 85. An O-ring 91 may be provided in a groove at the lower end of the threads in the cylindrical portion 64.

As shown in FIG. 3, the seal means 82 includes a seal member 93 mounted in a retainer 95 extending into a recess in the base 50 and having a flange disposed in a recess in a bushing 97 in the seal ring 54. An O-ring 99 is also provided in the recess in the bushing 97 around the flange on the retainer 95. The wiper seal 84 includes a seal member 101 mounted in the bushing 97 below the member 93 with a compression ring 103 being disposed between the seal members 93 and 103. Thus, the wiper seal 84 prevents foreign matter from being carried on the rod 34 into the seal means 82.

The low pressure region above the piston 66 and the piston rod 34 is connected to a drain cavity 86 provided in a control block 88 attached to one side of the base 50. A cylindrical tube 90 extends between the control block 88 and the cylinder head 52 which has a passageway 92 therein communicating with the tube 90. Fluid from the drain cavity 86 may be returned to a supply reservoir (not shown) through a conduit 94.

When the pressurized actuating fluid is admitted to the high pressure chamber 68, the annular piston 66 is forced upwardly to compress the spring means 38 and raise the valve member 28 from the valve seat 26. When the pressure fluid is released from the chamber 68 the piston 66 is force downwardly by the spring means 38, thereby closing the valve member 28.

In order to decrease the stroking time of the hydraulic actuator, it is essential that the actuating fluid be released from the high pressure chamber 68 quickly. This is accomplished by providing the dump valve 15. As shown, the high pressure chamber 68 is connected to the drain cavity 86 through an opening 96 in the base 50. When the dump valve is operated the pressurized actuating fluid is released into the drain cavity 86.

As shown more clearly in FIGS. 4 and 5, the dump valve 15 comprises a housing 98 attached to one side of the actuator control block 88 which, in turn, is attached to one side of the actuator base 50. The housing 98 has a generally cylindrical control fluid chamber 100 and a generally cylindrical exhaust chamber 102 therein. A valve member 104 for releasing the actuating fluid through the opening 96 in the base has a stem 106 slidably disposed in a bushing 108 mounted in the control block 88 which consititutes an end wall of the housing 98. The valve member 104 is held in its closed position by piston means 110 mounted on the valve stem 106 and separating the control fluid chamber from the exhaust chamber 102 to retain a pressurized control fluid in the control fluid chamber when the valve member 104 is closed.

The piston means comprises a disc-like feedback valve member 112 slidably disposed on the valve stem 106 between a shoulder 114 and a disc-like piston head 116 fixed on the valve stem 106 between a shoulder 118 and a sleeve 120. The sleeve 120 is secured on the valve stem 106 by a nut 121. The valve member 112 has an annular projection 122 at its outer periphery which seats on an end face 124 of an annular seating member 126 encircling the exhaust chamber 102 and having an inside diameter less than the diameter of the piston means 110. The diameter of the piston means is less than the diameter of the control fluid chamber 100. Thus, when the valve member 104 is in its open position, as shown in FIG. 5, the pressurized control fluid is permitted to flow from the control fluid chamber 100 into the exhaust chamber 102 and thence into the drain cavity 86 through passageways 128 provided in the bushing 108.

The structure and operation of the feedback valve member 112 are fully described in a US. Pat. No. 3,656,709 by Milton M. Hobbs and assigned to the same assignee as this application. As shown, an O-ring seal 130, composed of a resilient member, is disposed between a should 132 on the valve member 112 and an annular projection 134 on the piston head 116. When the dump valve member 104 is being held closed by fluid pressure in the control fluid chamber 100, the projection 134 compresses the resilient ring to hold the projection 122 on the valve member 112 in seating relation with the face 124 on the seating member 126. In this condition, the valve member 112 is spaced from the shoulder 114 on the valve stem 106.

- by a'distance 136. This space 136 allows the valve member 104 to move from its seated position against the base 50 to a slightly opened position in case the force on the valve member 104 from the actuating fluid in the high pressure chamber 68 is greater than the force of the control fluid in the chamber 100 on the piston head 116.

The slight movement of the valve member 104 relieves a transient condition which may occur when either the actuating fluid pressure temporarily increases to a higher value than it should, or when the control fluid pressure temporarily decreases to a lower value than it should. During this slight movement of the valve member 104, the feedback valve member 112 is maintained in seating engagement with the face 124 by the resilient force of the resilient member 130. Thus, the control fluid is retained in the control fluid chamber 100. An annular recess 138 and passageways 140 are provided in the valve member 112 to permit any fluid which may leak past the resilient member 130 to drain into the exhaust chamber 102.

In order to insure that the dump valve member 104 will be actuated to its fully opened position when the control fluid pressure in the control fluid chamber 100 is released, a helical compression spring 142 is disposed in the exhaust chamber 102 between the feedback valve 112 and the bushing 108 in the control block 88. Thus, the spring 142 cooperates with the pressurized actuating fluid in the high pressure chamber 68 to open the dump valve member 104. It will be understood that the dump valve member 104 might stop in an intermediate position after the valve member 104 is unseated from the base 50 and the actuating fluid is released into the drain cavity 86. However, the spring 142 actuates the valve member 104 to its fully opened position, thereby providing the full and maximum orifice area for the actuating fluid to flow into the drain.

cavity and permitting the annular piston 66 to drop quickly to its lowermost position. In this manner the stroking time of the actuator is reduced.

In order to provide a force for closing the dump valve member 104, the sleeve 120 on the valve stem 106 is slidably disposed in a cylindrical bore in a bushing 144 mounted in the end wall 146 of the housing 98. Thus, the sleeve 120 and the valve stem 106 constitute secondary piston means for actuating the piston means 110 into engagement with the seating member 126. As shown, restricted passageways 148 are provided in the cylindrical wall of the bushing 144. When the control fluid is admitted into the bushing 144 through a passageway 150, sufficient pressure is maintained within the bushing due to the restricted passageways 148 to cause the secondary piston 120 to drive the main piston 110 into engagement with the seating face 124 against the force of the spring 142. Once the piston means 110 is closed, it is held closed by the pressure of the control fluid which flows intothe control chamber 100 through the passageways 148. The areas of the main piston means 110 and the secondary piston means 120 are such that the valve member 104 is held closed against the pressure of the actuating fluid in the high pressure chamber 68 and the force of the spring 142.

From the foregoing description it is apparent that the invention provides a servo-actuator mechanism in which the high pressure of the servo-actuating fluid does not act on the piston rod seals which prevent the fluid from leaking from the actuator. Furthermore, the surface of the piston rod which contacts the seals is protected from mechanical damage. Therefore, the effectiveness of the seals is maintained. Also, the dump valve for the mechanism is driven open by the actuating fluid pressure and a spring force which insures that the dump valve is fully opened to provide maximum orifice area for releasing the actuating fluid, thereby reducing the stroking time of the actuator.

I claim: 1 A servo-actor mechanism, comprising a actuator cylinder structure, a piston movable rectilinearly in the cylinder structure, said cylinder structure having a high pressure chamber therein for receiving a pressurized fluid to apply pressure on the piston, a dump valve housing having a control fluid chamber and an exhaust chamber therein, a valve member for releasing the pressurized fluid from the high pressure chamber,

said valve member having a stem slidably disposed in the housing,

piston means mounted on the stem for holding the valve member in its closed position to block flow of the pressurized fluid from the high pressure chamber,

said piston means separating the control fluid chamber from the exhaust to retain pressurized control fluid in the control fluid chamber when the valve member is closed,

the diameter of the piston means being less than the diameter of the control fluid chamber to permit control fluid to flow from the control fluid chamber into the exhaust chamber during opening of the valve member, nd

spring means disposed in the exhaust chamber and cooperating with the pressurized fluid in the high pressure chamber to open the valve member when the control fluid pressure is released.

2. The mechanism defined in claim 1, including an annular seating member encircling the exhaust chamber and having an inside diameter less than the diameter of the piston means to provide an end face seat for the piston means when the valve member is closed.

3. The mechanism defined in claim 2, including secondary piston means mounted on the valve stem to actuate the piston means into engagement with said end face seat.

4. The mechanism defined in claim 3, including generally cylindrical means in the control fluid chamber receiving said secondary piston means. 

2. The mechanism defined in claim 1, including an annular seating member encircling the exhaust chamber and having an inside diameter less than the diameter of the piston means to provide an end face seat for the piston means when the valve member is closed.
 3. The mechanism defined in claim 2, including secondary piston means mounted on the valve stem to actuate the piston means into engagement with said end face seat.
 4. The mechanism defined in claim 3, including generally cylindrical means in the control fluid chamber receiving said secondary piston means. 